1. Technical Field
The present invention relates to a memory controller, a semiconductor integrated circuit device, a semiconductor device, a microcomputer, and an electronic device.
2. Related Art
Dynamic random access memory (DRAM) and a synchronous DRAM (SDRAM) require a periodic refresh. The SDRAM (DRAM) is a storing medium for recording data of input/output (I/O) depending on the presence of electric charge. Since electric charge is lost with time, recorded data needs to be refreshed periodically. The SDRAM (DRAM) has a simpler memory configuration compared to a SRAM and is suitable for larger capacity. Therefore, there is a case where a system requiring a relatively large memory capacity is configured using an SDRAM or both a flash memory and an SDRAM.
Here, when an SDRAM and an SRAM are used, there is a case where the two have a shared bus. In such a case, simultaneous access to the SDRAM and the SRAM is impossible because the two share a data bus and an address bus.
However, since the SDRAM requires periodic refresh, a request for refreshing the SDRAM may arise while the SRAM is accessed.
In such a case, there has been a problem that a refresh request arising during access to the SRAM is put into a waiting state until the access is completed and, on the other hand, a request for accessing the SRAM arising during refresh of the SDRAM is put into a waiting state until the refresh is completed.
There has been another problem that, in a configuration having priority in refreshing the SDRAM, access to the SDRAM is interrupted, leading to a degradation of system performance such as a reduction of data transfer rate, etc.
The present invention has been developed, taking the above problems into consideration, and aims to provide a memory controller, which enables the execution of refresh of the first memory even while the second memory is being accessed in a system configuration wherein the first memory requiring refresh and the second memory not requiring refresh share part of a bus, as well as a semiconductor integrated circuit device, a semiconductor device, a microcomputer, and an electronic device.